1. Field of the Invention
The present invention relates to a polarization-maintaining fiber that can be used in a temperature range of approximately −60 to +300° C. and an optical fiber sensor that uses this fiber.
Priority is claimed on Japanese Patent Application No. 2010-183215, filed Aug. 18, 2010, the content of which is incorporated herein by reference.
2. Background Art
In strain and temperature sensing technology using optical fibers, there is a problem in that, when strain and temperature change are induced simultaneously in an object to be measured, it is difficult to measure strain and temperature change discriminatively.
With respect to this problem, sensors that can measure strain and temperature simultaneously using a polarization maintaining fiber and a method thereof are disclosed in Japanese Patent No. 3819119 (refer to Patent Document 1), Japanese Patent No. 4420982 (refer to Patent Document 2), Japanese Patent No. 4474494 (refer to Patent Document 3), and “Strain and Temperature Multiplexed Measurement Sensor Utilizing Polarization Maintaining Fiber”, Koji Omichi, Daichi Wada, Hideaki Murayama, Hirotaka Igawa, IEICE Technical Report, Vol. 109, No. 175, OPE2009-97, pp. 117-122, August 2009 (refer to Non-Patent Document 1).
Patent Documents 1 to 3 and Non-patent Document 1 show that the upper limit of the measurable temperature is approximately +120° C. (a temperature change from room temperature is approximately 100° C.) (refer to FIG. 4 of Patent Document 1, paragraphs 0071 to 0072 of Patent Document 2, paragraphs 0095 to 0096 of Patent Document 3, and “4.2 Simultaneous measurement of strain and temperature” in Non-patent Document 1).
This is because a polarization-maintaining fiber that is used in the sensing portion is coated with a UV-curable (an ultraviolet curable) acrylate, and the heat resistant temperature of this coating layer is approximately +120° C.
However, there has increasingly been a demand to provide an optical fiber sensor that is capable of measuring strain and temperature change simultaneously beyond the above-described temperature range.
Specifically, the optical fiber sensor is required in a high temperature environment that is represented by oil wells (for example, +150 to +300° C.) and an environment with large temperature fluctuations represented by aircraft (for example, −60 to +120° C.).
In these fields of application, it is difficult to apply the optical fiber sensor due to the heat resistant temperature of the coating material as described above.